Flush data streams or indices Generally available

POST /_flush

Flushing a data stream or index is the process of making sure that any data that is currently only stored in the transaction log is also permanently stored in the Lucene index. When restarting, Elasticsearch replays any unflushed operations from the transaction log into the Lucene index to bring it back into the state that it was in before the restart. Elasticsearch automatically triggers flushes as needed, using heuristics that trade off the size of the unflushed transaction log against the cost of performing each flush.

After each operation has been flushed it is permanently stored in the Lucene index. This may mean that there is no need to maintain an additional copy of it in the transaction log. The transaction log is made up of multiple files, called generations, and Elasticsearch will delete any generation files when they are no longer needed, freeing up disk space.

It is also possible to trigger a flush on one or more indices using the flush API, although it is rare for users to need to call this API directly. If you call the flush API after indexing some documents then a successful response indicates that Elasticsearch has flushed all the documents that were indexed before the flush API was called.

Required authorization

  • Index privileges: maintenance

Query parameters

  • allow_no_indices boolean

    A setting that does two separate checks on the index expression. If false, the request returns an error (1) if any wildcard expression (including _all and *) resolves to zero matching indices or (2) if the complete set of resolved indices, aliases or data streams is empty after all expressions are evaluated. If true, index expressions that resolve to no indices are allowed and the request returns an empty result.

  • expand_wildcards string | array[string]

    Type of index that wildcard patterns can match. If the request can target data streams, this argument determines whether wildcard expressions match hidden data streams. Supports comma-separated values, such as open,hidden.

    Values are all, open, closed, hidden, or none.

  • force boolean

    If true, the request forces a flush even if there are no changes to commit to the index.

  • ignore_unavailable boolean

    If false, the request returns an error if it targets a concrete (non-wildcarded) index, alias, or data stream that is missing, closed, or otherwise unavailable. If true, unavailable concrete targets are silently ignored.

  • wait_if_ongoing boolean

    If true, the flush operation blocks until execution when another flush operation is running. If false, Elasticsearch returns an error if you request a flush when another flush operation is running.

Responses

  • 200 application/json
    Hide response attribute Show response attribute object
    • _shards object
      Hide _shards attributes Show _shards attributes object
      • failed number Required

        The number of shards the operation or search attempted to run on but failed.

      • successful number Required

        The number of shards the operation or search succeeded on.

      • total number Required

        The number of shards the operation or search will run on overall.

      • failures array[object]
        Hide failures attributes Show failures attributes object
        • index string
        • node string
        • reason object Required

          Cause and details about a request failure. This class defines the properties common to all error types. Additional details are also provided, that depend on the error type.

        • shard number
        • status string
        • primary boolean
      • skipped number
POST /_flush 
curl \
 --request POST 'http://api.example.com/_flush'